In order to adjust the position and the attitude, and to stabilize the orbital motion, of satellites and orbital space stations, such orbital spacecraft typically include rocket thrusters that effectuate the required corrective movements of the spacecraft by relatively small, exactly dosed or controlled thrust impulses. In order to operate these rocket thrusters, the spacecraft carry along appropriate propellant fuels which are usually stored in liquid form in suitable fuel tanks, as well as oxidizers if necessary, which are also stored in suitable tanks. In order to expel the liquid fuel and oxidizer out of the respective tanks in a positive-feed manner, it is generally known to use pressurized gases introduced into the tanks. However, this gives rise to the problem that the gaseous pressure medium can become mixed with the liquid fuel or oxidizer.
In order to allow the gaseous pressure medium to be separated from the liquid fuel or oxidizer, it is also known to separate the interior space of the fuel tank or oxidizer tank into two or more partial chambers by means of one or more flexible membranes. One of these partial chambers on one side of the membrane contains the liquid fuel or oxidizer, while the other partial chamber on the other side of the membrane is filled with and pressurized by the gaseous pressure medium. When the pressure medium is supplied into the respective partial chamber and pressurized, it flexibly deflects the dividing membrane and thus exerts a corresponding supply pressure onto the liquid fuel or oxidizer so as to push the liquid fuel or oxidizer out of the tank.
Especially when the tank is to be used to store a rocket or satellite fuel based on hydrazine, or an oxidizer based on nitrogen tetroxide, the membrane for separating these liquid media from the gaseous pressurizing medium is typically a polymeric membrane, because the polymer materials provide relatively good separation, resistance to chemical attack by the media being stored, and long term durability even under the repeated flexing conditions that come into play.
However, such polymeric membranes cannot completely prevent the permeation of vapors of the liquid fuel or oxidizer through the membrane and into the partial chamber containing the gaseous pressure medium. Such a permeation process is especially caused or enhanced due to the temperature variations that are unavoidable in every technical system of this type, and the influence of these temperature variations on the differing thermal capacities of the liquid fuel or oxidizer relative to the gaseous pressure medium. As a result, the fuel or oxidizer vapors that permeate through the membrane ultimately condense in the partial chamber containing the gaseous pressure medium. The condensed liquid then becomes trapped, so to speak, in the gas-containing partial chamber and cannot be supplied to the associated rocket engine. Since this permeation and condensation can occur continuously, the result can be a considerable loss of useable fuel or oxidizer.
The above described problem of permeation of the fuel or oxidizer through the membrane could be prevented by using a membrane of a non-permeable material rather than the permeable polymers that are conventionally used. The requirements of non-permeability would essentially only be satisfied by providing metal membranes, but such metal membranes are mechanically not suitable for this application because they would suffer metal fatigue and crack formation as a result of the substantial repetitious deformation or deflection processes with a great extent of deformation, to which such dividing membranes are subjected during operation.